Array substrate for display device and method of fabricating the same

ABSTRACT

An array substrate for a display device includes: a substrate; first and second gate electrodes of impurity-doped polycrystalline silicon on the substrate; a gate insulating layer on the first and second gate electrodes; first and second active layers of intrinsic polycrystalline silicon on the gate insulating layer, the first and second active layers corresponding to the first and second active layers, respectively; an interlayer insulating layer on the first and second active layers and including first to fourth active contact holes, the first and second active contact holes exposing side portions of the first active layer, the third and fourth active contact holes exposing side portions of the second active layer; first and second ohmic contact layers of impurity-doped amorphous silicon on the interlayer insulating layer, the first ohmic contact layer contacting the first active layer through the first and second active contact holes, the second ohmic contact layer contacting the second active layer through the third and fourth active contact hole; first source and drain electrodes on the first ohmic contact layer and second source and drain electrodes on the second ohmic contact layer; a data line on the interlayer insulating layer, the data line connected to the first source electrode; a first passivation layer on the first source and drain electrodes, the second source and drain electrodes and the data line; a gate line on the first passivation layer, the gate line connected to the first gate electrode and crossing the data line to define a pixel region; a second passivation layer on the gate line; and a pixel electrode on the second passivation layer, the pixel electrode connected to the second drain electrode.

The present invention claims the benefit of Korean Patent ApplicationNo. 10-2009-0094007, filed in Korea on Oct. 1, 2009, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an array substrate for a displaydevice, and more particularly, to an array substrate including a thinfilm transistor and a storage capacitor and a method of fabricating thearray substrate.

2. Discussion of the Related Art

As information technology progresses, flat panel display (FPD) deviceshaving light weight, thin profile and low power consumption have beendeveloped. Specifically, a cathode ray tube (CRT) has been replaced bythe FPD devices such as a liquid crystal display (LCD) device or anorganic electroluminescent display (ELD) device.

The LCD devices use the optical anisotropy and polarization propertiesof liquid crystal molecules to produce an image. Among various types LCDdevices, an active matrix type liquid crystal display (AM-LCD) devicewhere a thin film transistor (TFT) is formed in each pixel region as aswitching element turning on/off a voltage has been the subject ofrecent research due to its high resolution and superior quality fordisplaying moving images.

The organic ELD devices have a high brightness and a low drivingvoltage. In addition, since the organic ELD devices are an emissivetype, the organic ELD devices have a high contrast ratio and a thinprofile. Also, the organic ELD devices can display images withoutviewing angle limitations. Further, since the organic ELD devices have ashort response time of several microseconds (μs), the organic ELDdevices have a stable operation property at a low temperature and anadvantage in displaying moving images. Moreover, since the organic ELDdevices are driven with a relatively low voltage of about 5 V to about15 V, the organic ELD devices have advantages in design and fabricationof a driving circuit.

Each of an AM-LCD device and an organic ELD device includes an arraysubstrate having a thin film transistor (TFT) in each pixel region as aswitching element for controlling a data signal application.Specifically, the array substrate of the organic ELD device further hasa driving TFT for driving an organic electroluminescent (EL) diode ineach pixel region.

FIG. 1 is a cross-sectional view showing an array substrate for adisplay device according to the related art. In FIG. 1, a gate electrode15 and a gate line (not shown) are formed on a substrate 11 having apixel region P, and a gate insulating layer 18 is formed on the gateelectrode 15 and the gate line. A semiconductor layer 28 including anactive layer 22 of intrinsic amorphous silicon and an ohmic contactlayer 26 of impurity-doped amorphous silicon is formed on the gateinsulating layer 18 over the gate electrode 15. In addition, source anddrain electrodes 36 and 38 spaced apart from each other are formed onthe ohmic contact layer 26, and a data line 33 is formed over the gateinsulating layer 18. A semiconductor pattern 29 including first andsecond patterns 27 and 23 is formed between the data line 33 and thegate insulating layer 18.

The gate electrode 15, the gate insulating layer 18, the semiconductorlayer 28, the source electrode 36 and the drain electrode 38 constitutea thin film transistor (TFT) Tr. When the display device is an organicelectroluminescent display device, the TFT Tr may function as a drivingTFT, and a switching TFT (not shown) connected to the gate line, thedata line 33 and the TFT Tr may be formed in the pixel region P.Further, a passivation layer 42 is formed on the source and drainelectrodes 36 and 38, and a pixel electrode 50 is formed on thepassivation layer 42 in the pixel region P. The passivation layer 42includes a drain contact hole 45 exposing the drain electrode 38, andthe pixel electrode 50 is connected to the drain electrode 38 throughthe drain contact hole 45.

In the TFT Tr, the active layer 22 of the semiconductor layer 28includes a first portion exposed between the ohmic contact layer 26 anda second portion under the ohmic contact layer 26. The first portion ofthe active layer 22 has a first thickness t1 and the second portion ofthe active layer 22 has a second thickness t2 different from the firstthickness t2 (t1≠t2). The difference between the first and secondthicknesses t1 and t2 cause deterioration of the TFT Tr.

FIG. 2 is a cross-sectional showing a step of forming a semiconductorlayer, a source electrode and a drain electrode of an array substratefor a display device according to the related art. Although not shown inFIG. 2, an active layer, an impurity-doped amorphous silicon pattern anda source-drain pattern are formed on a substrate 11 by patterning anintrinsic amorphous silicon layer, an impurity-doped amorphous siliconlayer and a metal layer. Next, source and drain electrodes 36 and 38 areformed by patterning the source-drain pattern, and the impurity-dopedamorphous silicon pattern is exposed between the source and drainelectrodes 36 and 38.

In FIG. 2, the impurity-doped amorphous silicon pattern exposed betweenthe source and drain electrodes 36 and 38 is removed by a dry etchingmethod to form an ohmic contact layer 26 under the source and drainelectrodes 36 and 38. When the dry etching step is performed for ainsufficient time, the impurity-doped amorphous silicon pattern exposedbetween the source and drain electrodes 36 and 38 may remain on theactive layer 26 and the remaining impurity-doped amorphous siliconpattern may deteriorate a thin film transistor (TFT) Tr (of FIG. 1).Accordingly, the dry etching step is performed for a sufficient time toremove the impurity-doped amorphous silicon pattern exposed between thesource and drain electrodes 36 and 38 completely and the active layer 22under the impurity-doped amorphous silicon pattern is partially removed.As a result, the active layer 22 includes a first portion that isexposed between the source and drain electrodes 36 and 38 and has afirst thickness t1 and a second portion that is under the ohmic contactlayer 26 and has a second thickness t2 different from the firstthickness (t1≠t2).

However, the thickness difference between the first and second portionsof the active layer 22 deteriorates the TFT Tr. In addition, since theintrinsic amorphous silicon layer is formed to have a sufficientthickness over about 1000 Å based on the partial removal of the activelayer 22 in the dry etching step, the deposition time for the intrinsicamorphous silicon layer increases and productivity is reduced.

In an array substrate for a display device such as an AM-LCD device andan organic ELD device, a thin film transistor (TFT) is connected to agate line, a data line and a pixel electrode in each pixel region andapplies a data signal to the pixel electrode selectively andperiodically. The TFT includes an active layer and the active layer maybe formed of amorphous silicon or polycrystalline silicon. Sinceamorphous silicon has a random atomic arrangement, amorphous silicon hasa transition from a stable state to a quasi-stable state when light isirradiated or when an electric field is applied. Accordingly, the TFTincluding an active layer of amorphous silicon has problems instability. In addition, since amorphous silicon has relatively lowcarrier mobility within a range of about 0.1 cm²/Vs to about 1.0 cm²/Vsin a channel region, the TFT including an active layer of amorphoussilicon has problems in use as an element of a driving circuit.

To solve the above problems of amorphous silicon, the TFT including anactive layer of polycrystalline silicon has been suggested. For example,amorphous silicon for a semiconductor layer may be crystallized tobecome polycrystalline by a crystallization method using a laserapparatus.

FIG. 3 is a cross-sectional view showing an array substrate including apolycrystalline silicon thin film transistor according to the relatedart. In FIG. 3, a buffer layer 53 is formed on a substrate 51, and asemiconductor layer 55 of polycrystalline silicon is formed on thebuffer layer 53. The semiconductor layer 55 includes an active region 55a of intrinsic polycrystalline silicon and a source-drain region 55 b ofimpurity-doped polycrystalline silicon at both sides of the activeregion 55 a. The source-drain region 55 b may include one of negativetype impurities of high concentration (n+) and positive type impuritiesof high concentration (p+).

A gate insulating layer 58 is formed on the semiconductor layer 55, anda gate electrode 59 is formed on the gate insulating layer 58 over thesemiconductor layer 55. In addition, an interlayer insulating layer 61is formed on the gate electrode 59, and source and drain electrodes 70and 72 are formed on the interlayer insulating layer 61. The interlayerinsulating layer 61 and the gate insulating layer 58 include first andsecond semiconductor contact holes 63 and 64 exposing the source-drainregion 55 b, and the source and drain electrodes 70 and 72 are connectedto the source-drain region 55 b through the first and secondsemiconductor contact holes 63 and 64, respectively. A passivation layer75 is formed on the source and drain electrodes 70 and 72, and a pixelelectrode 82 is formed on the passivation layer 75. The passivationlayer 75 includes a drain contact hole 78 exposing the drain electrode72, and the pixel electrode 82 is connected to the drain electrode 78through the drain contact hole 78.

The source-drain region 55 b may be formed by doping the semiconductorlayer of intrinsic polycrystalline silicon with the impurities, and thedoping step may be performed using an ion implantation apparatus.Accordingly, an additional apparatus is required for fabricating apolycrystalline silicon TFT and fabrication cost increases.

Further, when a bottom gate structure where a gate electrode is under asemiconductor layer is applied to a polycrystalline silicon TFT, acrystallization step having a relatively high process temperature isperformed for a semiconductor layer of amorphous silicon over a gateelectrode. Since the gate electrode is formed of a metallic material,the gate electrode may be degraded during the crystallization step.

Moreover, as a display device having higher quality and higherresolution is required, a size of a pixel region is reduced. As aresult, a sufficient capacitance of a storage capacitor withoutreduction of aperture ratio has been the subject of recent research anddevelopment.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an array substrate fora display device and a method of fabricating the same that substantiallyobviate one or more of the problems due to limitations and disadvantagesof the related art.

An object of the present invention is to provide an array substrate fora display device where a property of a thin film transistor is improvedby protecting an active layer during a dry etching step and forming asemiconductor layer of polycrystalline silicon without a doping step anda method of fabricating the array substrate.

Another object of the present invention is to provide an array substratefor a display device where a thin film transistor has a bottom gatestructure due to a gate electrode of polycrystalline silicon and amethod of fabricating the array substrate.

Another object of the present invention is to provide an array substratefor a display device where a sufficient capacitance of a storagecapacitor is obtained without reduction of aperture ratio and a methodof fabricating the array substrate.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein, anarray substrate for a display device includes: a substrate; first andsecond gate electrodes of impurity-doped polycrystalline silicon on thesubstrate; a gate insulating layer on the first and second gateelectrodes; first and second active layers of intrinsic polycrystallinesilicon on the gate insulating layer, the first and second active layerscorresponding to the first and second active layers, respectively; aninterlayer insulating layer on the first and second active layers andincluding first to fourth active contact holes, the first and secondactive contact holes exposing side portions of the first active layer,the third and fourth active contact holes exposing side portions of thesecond active layer; first and second ohmic contact layers ofimpurity-doped amorphous silicon on the interlayer insulating layer, thefirst ohmic contact layer contacting the first active layer through thefirst and second active contact holes, the second ohmic contact layercontacting the second active layer through the third and fourth activecontact hole; first source and drain electrodes on the first ohmiccontact layer and second source and drain electrodes on the second ohmiccontact layer; a data line on the interlayer insulating layer, the dataline connected to the first source electrode; a first passivation layeron the first source and drain electrodes, the second source and drainelectrodes and the data line; a gate line on the first passivationlayer, the gate line connected to the first gate electrode and crossingthe data line to define a pixel region; a second passivation layer onthe gate line; and a pixel electrode on the second passivation layer,the pixel electrode connected to the second drain electrode.

In another aspect, a method of fabricating an array substrate for adisplay device includes: sequentially forming a first impurity-dopedamorphous silicon layer, a first inorganic insulating layer and anintrinsic amorphous silicon layer on a substrate; crystallizing thefirst impurity-doped amorphous silicon layer and the intrinsic amorphoussilicon layer to form an impurity-doped polycrystalline silicon layerand an intrinsic polycrystalline silicon layer; patterning theimpurity-doped polycrystalline silicon layer, the first organicinsulating layer and the intrinsic polycrystalline silicon layer to forma first gate electrode, a gate insulating layer and a first active layerof polycrystalline silicon sequentially on the substrate and a secondgate electrode, the gate insulating layer and a second active layer ofpolycrystalline silicon sequentially on the substrate; forming aninterlayer insulating layer on the first and second active layers, theinterlayer insulating layer including first to fourth active contactholes, the first and second active contact holes exposing side portionsof the first active layer, the third and fourth active contact holesexposing side portions of the second active layer; sequentially forminga second impurity-doped amorphous silicon layer and a first metal layeron the interlayer insulating layer; pattering the second impurity-dopedamorphous silicon layer and the first metal layer to form first andsecond ohmic contact layers, first source and drain electrodes on thefirst ohmic contact layer, second source and drain electrodes on thesecond ohmic contact layer and a data line on the interlayer insulatinglayer, the first ohmic contact layer contacting the first active layerthrough the first and second active contact holes, the second ohmiccontact layer contacting the second active layer through the third andfourth active contact hole; forming a first passivation layer on thefirst source and drain electrodes, the second source and drainelectrodes and the data line; forming a gate line on the firstpassivation layer, the gate line connected to the first gate electrodeand crossing the data line to define a pixel region; forming a secondpassivation layer on the gate line; and forming a pixel electrode on thesecond passivation layer, the pixel electrode connected to the seconddrain electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross-sectional view showing an array substrate for adisplay device according to the related art;

FIG. 2 is a cross-sectional showing a step of forming a semiconductorlayer, a source electrode and a drain electrode of an array substratefor a display device according to the related art;

FIG. 3 is a cross-sectional view showing an array substrate including apolycrystalline silicon thin film transistor according to the relatedart;

FIG. 4 is a plan view showing an array substrate for an organicelectroluminescent display device according to a first embodiment of thepresent invention;

FIG. 5 is a cross-sectional view, which is taken along a line V-V ofFIG. 4, showing an array substrate for an organic electroluminescentdisplay device according to a first embodiment of the present invention;

FIG. 6 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a secondembodiment of the present invention;

FIG. 7 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a thirdembodiment of the present invention;

FIG. 8 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a fourthembodiment of the present invention;

FIG. 9 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a fifthembodiment of the present invention; and

FIG. 10 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a sixthembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, which are illustrated in the accompanyingdrawings.

FIG. 4 is a plan view showing an array substrate for an organicelectroluminescent display device according to a first embodiment of thepresent invention.

In FIG. 4, a gate line 145, a data line 130 and a power line 148 areformed on a substrate 101. The gate line 145 and the data line 130 crosseach other to define a pixel region P, and the power line 148 is spacedapart from the gate line 145. A power electrode 134 connected to thepower line 148 through a power contact hole 154 is formed to be parallelto the data line 130.

In addition, a switching thin film transistor (TFT) STr and a drivingTFT DTr connected to each other are formed in the pixel region P. Theswitching TFT STr includes a first gate electrode 105 a, a first activelayer 115 a, a first source electrode 133 a and a first drain electrode136 a, and the driving TFT DTr includes a second gate electrode 105 b, asecond active layer 115 b, a second source electrode 133 b and a seconddrain electrode 136 b. The first gate electrode 105 a is connected tothe gate line 145 through a first gate contact hole 142 a, and the firstsource electrode 133 a is connected to the data line 130. A gateauxiliary pattern 146 is connected to the second gate electrode 105 bthrough a second gate contact hole 142 b, and a gate connectingelectrode 172 is connected to the first drain electrode 136 a through afirst drain contact hole 152 a and to the gate auxiliary pattern 146through an auxiliary contact hole 153. The second source electrode 133 bextends to the power electrode 134.

Further, a pixel electrode 170 is formed in the pixel region, and anorganic luminescent layer (not shown) is formed on the pixel electrode170. The pixel electrode 170 is connected to the second drain electrode136 b through a second drain contact hole 152 b. The organic luminescentlayer emits one of red, green and blue colored lights and the organicluminescent layers emitting different colored lights may be alternatelydisposed in the pixel regions P. A reference electrode (not shown) isformed on the organic luminescent layer. The reference electrode may beformed over an entire surface of the substrate 101.

The power electrode 134 overlaps the second gate electrode 105 b with agate insulating layer (not shown) and an interlayer insulating layer(not shown) interposed therebetween to constitute a storage capacitorStgC. In addition, the pixel electrode 170, the organic luminescentlayer and the reference electrode constitute an organicelectroluminescent (EL) diode (not shown). For example, the pixelelectrode 170 may function as an anode of the organic EL diode andinclude a transparent conductive material having a relatively high workfunction. The reference electrode may function as a cathode of theorganic EL diode and include a metallic material having a relatively lowwork function. Although not shown in FIG. 4, a bank of one of inorganicand organic insulating materials is formed at a boundary portion of thepixel region P. The bank overlaps the pixel electrode 170 to separatethe organic luminescent layers in adjacent pixel regions P and toprevent an electric shortage between the pixel electrode 170 and thereference electrode.

FIG. 5 is a cross-sectional view, which is taken along a line V-V ofFIG. 4, showing an array substrate for an organic electroluminescentdisplay device according to a first embodiment of the present invention.

In FIG. 5, a buffer layer 102 of an inorganic insulating material isformed on an entire surface of a substrate 101, and first and secondgate electrodes 105 a and 105 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 102. A gateinsulating layer 109 of an inorganic insulating material is formed onthe first and second gate electrodes 105 a and 105 b, and first andsecond active layers 115 a and 115 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 109. Thefirst and second active layers 115 a and 115 b are formed over the firstand second gate electrodes 105 a and 105 b, respectively.

In addition, an interlayer insulating layer 122 including first tofourth active contact holes 123 a, 123 b, 123 c and 123 d is formed onthe first and second active layers 115 a and 115 b. The first and secondactive contact holes 123 a and 123 b expos side portions of the firstactive layer 115 a, respectively, and the third and fourth activecontact holes 123 c and 123 d expose side portions of the second activelayer 115 b, respectively. First and second ohmic contact layers 127 aand 127 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 122. The first ohmic contact layer 127 a isconnected to the side portions of the first active layer 115 a throughthe first and second active contact holes 123 a and 123 b, and thesecond ohmic contact layer 127 b is connected to the side portions ofthe second active layer 115 b through the third and fourth activecontact holes 123 c and 123 d. A first source electrode 133 a and afirst drain electrode 136 a spaced apart from each other are formed onthe first ohmic contact layer 127 a, and a second source electrode 133 band a second drain electrode 136 b spaced apart from each other areformed on the second ohmic contact layer 127 b. In addition, a powerelectrode 134 is formed on the second ohmic contact layer 127 b. Thesecond source electrode 133 b extends to the power electrode 134 and thepower electrode 134 is connected to a power line 148 (of FIG. 4). A dataline 130 (of FIG. 4) connected to the first source electrode 133 a isformed on the interlayer insulating layer 122.

The power electrode 134 and the second gate electrode 105 b overlap eachother with the gate insulating layer 109 and the interlayer insulatinglayer 122 interposed therebetween to constitute a storage capacitorStgC. In addition, the first gate electrode 105 a, the gate insulatinglayer 109, the first active layer 115 a, the first ohmic contact layer127 a, the first source electrode 133 a and the first drain electrode136 a constitute a switching thin film transistor (TFT) STr, and thesecond gate electrode 105 b, the gate insulating layer 109, the secondactive layer 115 b, the second ohmic contact layer 127 b, the secondsource electrode 133 b and the second drain electrode 136 b constitute adriving TFT DTr.

Further, a first passivation layer 140 of an inorganic insulatingmaterial is formed on the first source electrode 133 a, the first drainelectrode 136 a, the second source electrode 133 b, the second drainelectrode 136 b and the data line. The first passivation layer 140, theinterlayer insulating layer 122 and the gate insulating layer 109include first and second gate contact holes 142 a and 142 b exposing thefirst and second gate electrodes 105 a and 105 b, respectively. Althoughnot shown in FIG. 5, the first passivation layer 140 includes a powercontact hole exposing the power electrode 134 extending from the secondsource electrode 133 b.

A gate line 145 and a gate auxiliary pattern 146 are formed on the firstpassivation layer 140. The gate line 145 crosses the data line to definea pixel region P and is connected to the first gate electrode 105 athrough the first gate contact hole 142 a. The gate auxiliary pattern146 is connected to the second gate electrode 105 b through the secondgate contact hole 142 b. The power line 148 (of FIG. 4) parallel to thegate line 145 is formed on the first passivation layer 140. The powerline 148 is connected to the power electrode 134 through the powercontact hole.

Moreover, a second passivation layer 150 of an inorganic insulatingmaterial is formed on the gate line 145 and the gate auxiliary pattern146. The second passivation layer 150 includes an auxiliary contact hole153 exposing the gate auxiliary pattern 146. In addition, the secondpassivation layer 150 and the first passivation layer 140 include firstand second drain contact holes 152 a and 152 b exposing the first andsecond drain electrodes 136 a and 136 b, respectively.

A pixel electrode 170 and a gate connecting electrode 172 each includinga transparent conductive material are formed on the second passivationlayer 150. The pixel electrode 170 is connected to the second drainelectrode 136 b through the second drain contact hole 152 b. Inaddition, the gate connecting electrode 172 is connected to the firstdrain electrode 136 a through the first drain contact hole 152 a and tothe gate auxiliary pattern 146 through the auxiliary contact hole 153.

Although not shown in FIG. 5, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 150 and thegate connecting electrode 172. In addition, an organic luminescent layeris formed on the pixel electrode 170 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 101. The pixel electrode 170, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

A method of fabricating an array substrate for an organicelectroluminescent display device according to a first embodiment of thepresent invention will be illustrated hereinafter with reference toFIGS. 4 and 5.

In FIGS. 4 and 5, the buffer layer 102 is formed on the substrate 101 bydepositing an inorganic insulating material such as silicon nitride(SiNx) and silicon oxide (SiO₂). Impurities such as alkali ions mayerupt from the substrate 101 during a subsequent crystallization stepfor the first and second active layers 615 a and 615 b, for example, asolid phase crystallization (SPC) step with a process temperature ofabout 600° C. to about 800° C., and the first and second active layers115 a and 115 b of polycrystalline silicon may be deteriorated by theimpurities. The buffer layer 102 shields the impurities and prevents thedeterioration of the first and second active layers 115 a and 115 b.

A first impurity-doped amorphous silicon layer (not shown), a firstinorganic insulating layer (not shown) and an intrinsic amorphoussilicon layer (not shown) are sequentially formed on the buffer layer102 by sequentially depositing impurity-doped amorphous silicon, aninorganic insulating material such as silicon nitride (SiNx) and siliconoxide (SiO₂) and intrinsic amorphous silicon. Since channel regions ofthe first and second active layers 115 a and 115 b are protected by theinterlayer insulating layer 122 during the dry etching step for thefirst to fourth active contact holes 123 a, 123 b, 123 c and 123 d, thethickness difference of the first and second active layers 115 a and 115b is prevented. Accordingly, the intrinsic amorphous silicon layer maybe formed to have a thickness of about 300 Å to about 1000 Å.

Next, an impurity-doped polycrystalline silicon layer (not shown) and anintrinsic polycrystalline silicon layer (not shown) are formed bycrystallizing the first impurity-doped amorphous silicon layer and theintrinsic amorphous silicon layer through the solid phasecrystallization (SPC) method. For example, a thermal crystallizationmethod under a process temperature of about 600° C. to about 800° C. oran alternating magnetic field crystallization method under a processtemperature of about 600° C. to 700° C. may be used for thecrystallization.

Next, the first gate electrode 105 a, the gate insulating layer 109 anda first polycrystalline silicon pattern (not shown) and the second gateelectrode 105 b, the gate insulating layer 109 and a secondpolycrystalline silicon pattern (not shown) are formed by patterning theimpurity-doped polycrystalline silicon layer, the first inorganicinsulating layer and the intrinsic polycrystalline silicon layer. Thefirst gate electrode 105 a, the gate insulating layer 109 and the firstpolycrystalline silicon pattern have the same shape as each other, andthe second gate electrode 105 b, the gate insulating layer 109 and thesecond polycrystalline silicon pattern have the same shape as eachother.

In a bottom gate type polycrystalline silicon TFT, a gate electrode of ametallic material is deteriorated during the crystallization step for anactive layer. For example, the gate electrode of a metallic material maybe deformed or the metallic material may be diffused through the gateinsulating layer into the active layer, which is referred to as aspiking, during the crystallization step having a process temperature ofabout 600° C. Since the first and second gate electrodes 105 a and 105 bare formed of impurity-doped amorphous silicon, deterioration of thefirst and second gate electrodes 105 a and 105 b during thecrystallization step is prevented.

Next, the first and second active layers 115 a and 115 b of intrinsicpolycrystalline silicon are formed by patterning the first and secondintrinsic polycrystalline silicon patterns. In addition, the interlayerinsulating layer 122 is formed on the first and second active layers 115a and 115 b by depositing an inorganic insulating material such assilicon nitride (SiNx) and silicon oxide (SiO₂), and the first, second,third and fourth active contact holes 123 a, 123 b, 123 c and 123 d areformed by patterning the interlayer insulating layer 122. The first andsecond active contact holes 123 a and 123 b expose the side portions ofthe first active layer 115 a, and the third and fourth active contactholes 123 c and 123 d expose the side portions of the second activelayer 115 b. Since the interlayer insulating layer 122 covering thecentral portion of the first and second active layers 115 a and 115 bfunctions as an etch stopper during the step of forming the first,second, third and fourth active contact holes 123 a, 123 b, 123 c and123 d, the thickness difference or the deterioration of the first andsecond active layers 115 a and 115 b is prevented.

Next, a second impurity-doped amorphous silicon layer (not shown) isformed on the interlayer insulating layer 122 by depositingimpurity-doped amorphous silicon, and a first metal layer (not shown) isformed on the second impurity-doped amorphous silicon layer bydepositing a first metallic material such as molybdenum (Mo), chromium(Cr) and molybdenum titanium (MoTi). The data line (not shown), thefirst ohmic contact layer 127 a, the first source electrode 133 a, thefirst drain electrode 136 a, the second ohmic contact layer 127 b, thesecond source electrode 133 b, the second drain electrode 136 b, thepower electrode 134 are formed by patterning the first metal layer andthe second impurity-doped amorphous silicon layer. Each of the data lineand the power electrode 134 includes a dummy pattern of impurity-dopedamorphous silicon. The first ohmic contact layer 127 a contacts thefirst active layer 115 a through the first and second active contactholes 123 a and 123 b, and the second ohmic contact layer 127 b contactsthe second active layer 115 b through the third and fourth activecontact holes 123 c and 123 d. The first source and drain electrodes 133a and 136 a are formed on the first ohmic contact layer 127 a, and thesecond source and drain electrodes 133 b and 136 b are formed on thesecond ohmic contact layer 127 b.

In another embodiment, a barrier layer of intrinsic amorphous siliconmay be formed under the second impurity-doped amorphous silicon layer.The barrier layer may be disposed between the first active layer 115 aand the first ohmic contact layer 127 a in the first and second activecontact holes 123 a and 123 b and between the second active layer 115 band the second ohmic contact layer 127 b in the third and fourth activecontact holes 123 c and 123 d. Since the adhesion between intrinsicpolycrystalline silicon and intrinsic amorphous silicon is better thanthe adhesion between intrinsic polycrystalline silicon andimpurity-doped amorphous silicon, the adhesion and the contactresistance between each of the first and second active layers 115 a and115 b and each of the first and second ohmic contact layers 127 a and127 b may be improved by the barrier layer. The barrier layer may bepatterned together with the first and second ohmic contact layers 127 aand 127 b to have the same shape as the ohmic contact layers 127 a and127 b.

Moreover, before the first and second ohmic contact layers 127 a and 127b or the barrier layer is formed on the interlayer insulating layer 122,a cleaning step using a buffered oxide etchant (BOE) may be performedfor the substrate 101 having the interlayer insulating layer. During thecrystallization step having a process temperature of about 600° C. toabout 800° C., a surface of the first and second active layers 115 a and115 b is oxidized and a thin thermal oxide film is formed on the firstand second active layers 115 a and 115 b. The contact property betweeneach of the first and second active layers 115 a and 115 b and each ofthe first and second ohmic contact layers 127 a and 127 b or betweeneach of the first and second active layers 115 a and 115 b and thebarrier layer may be degraded by the thin thermal oxide film.Accordingly, the thin thermal oxide film exposed through the first,second, third and fourth active contact holes 123 a, 123 b, 123 c and123 d may be removed through the cleaning step using a BOE.

The first gate electrode 105 a, the gate insulating layer 109, the firstactive layer 115 a, the first ohmic contact layer 127 a, the firstsource electrode 133 a and the first drain electrode 136 a constitute aswitching thin film transistor (TFT) STr, and the second gate electrode105 b, the gate insulating layer 109, the second active layer 115 b, thesecond ohmic contact layer 127 b, the second source electrode 133 b andthe second drain electrode 136 b constitute a driving TFT DTr. Inaddition, the second gate electrode 105 b, the gate insulating layer109, the interlayer insulating layer 122 and the power electrode 134overlapping each other constitute a storage capacitor StgC.

Next, the first passivation layer 140 is formed on the first sourceelectrode 133 a, the first drain electrode 136 a, the second sourceelectrode 133 b, the second drain electrode 136 b and the data line bydepositing an inorganic insulating material such as silicon nitride(SiNx) and silicon oxide (SiO₂), and first and second gate contact holes142 a and 142 b are formed by patterning the first passivation layer140, the interlayer insulating layer 122 and the gate insulating layer109. The first and second gate contact holes 142 a and 142 b expose thefirst and second gate electrodes 105 a and 105 b, respectively. Inaddition, the power contact hole 154 exposing the power electrode 134 isformed by patterning the first passivation layer 140.

Next, a second metal layer (not shown) is formed on the firstpassivation layer by depositing a second metallic material such asaluminum (Al), aluminum alloy (e.g., aluminum neodymium (AlNd)), copper(Cu), copper alloy, molybdenum (Mo) and chromium (Cr), and the gate line145, the gate auxiliary pattern 146 and the power line 148 are formed bypatterning the second metal layer. The power line 148 is connected tothe power electrode 134 through the power contact hole 154.

Next, the second passivation layer 150 is formed on the gate line 145,the gate auxiliary pattern 146 and the power line 148 by depositing aninorganic insulating material such as silicon nitride (SiNx) and siliconoxide (SiO₂), and the first and second drain contact holes 152 a and 152b are formed by patterning the second passivation layer 150 and thefirst passivation layer 140. The first and second drain contact holes152 a and 152 b expose the first and second drain electrodes 136 a and136 b, respectively. In addition, the auxiliary contact hole 153exposing the gate auxiliary pattern 146 is formed by patterning thesecond passivation layer 150.

Next, the pixel electrode 170 and the gate connecting electrode 172 areformed on the second passivation layer 150 by depositing and patterninga transparent conductive material such as indium-tin-oxide (ITO) andindium-zinc-oxide (IZO). The pixel electrode 170 is connected to thesecond drain electrode 136 b through the second drain contact hole 152b, and the gate connecting electrode 172 is connected to the first drainelectrode 136 a through the first drain contact hole 152 a and to thegate auxiliary pattern 146 through the auxiliary contact hole 153.

Next, the bank (not shown) is formed on an edge portion of the pixelelectrode 170 by depositing or coating one of inorganic and organicinsulating materials, and the organic luminescent layer (not shown) isformed on the bank and the pixel electrode 170. In addition, thereference electrode (not shown) is formed on the organic luminescentlayer.

In the organic ELD device according to the first embodiment of thepresent invention, since the first and second active layers 115 a and115 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 105 a and 105 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 115 a and 115 b is performed withoutdeformation of the first and second gate electrodes 105 a and 105 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 122 on a centralportion of the first and second active layers 115 a and 115 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 115 a and 115 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 127 a and 127 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 134 extending from the second sourceelectrode 133 b and connected to the power line 148 (of FIG. 4) overlapsthe second gate electrode 105 b with the gate insulating layer 109 andthe interlayer insulating layer 122 interposed therebetween toconstitute the storage capacitor StgC. As the resolution of the organicELD device increases, a size of the storage capacitor StgC decreases anda capacitance of the storage capacitor StgC also decreases. In anotherembodiment, a structure of the storage capacitor StgC is changed toobtain a sufficient capacitance.

FIG. 6 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a secondembodiment of the present invention.

In FIG. 6, a buffer layer 202 of an inorganic insulating material isformed on an entire surface of a substrate 201, and first and secondgate electrodes 205 a and 205 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 202. A gateinsulating layer 209 of an inorganic insulating material is formed onthe first and second gate electrodes 205 a and 205 b, and first andsecond active layers 215 a and 215 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 209. Thefirst and second active layers 215 a and 215 b are formed over the firstand second gate electrodes 205 a and 205 b, respectively.

In addition, an interlayer insulating layer 222 including first tofourth active contact holes 223 a, 223 b, 223 c and 223 d is formed onthe first and second active layers 215 a and 215 b. The first and secondactive contact holes 223 a and 223 b expos side portions of the firstactive layer 215 a, respectively, and the third and fourth activecontact holes 223 c and 223 d expose side portions of the second activelayer 215 b, respectively. First and second ohmic contact layers 227 aand 227 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 222. The first ohmic contact layer 227 a isconnected to the side portions of the first active layer 215 a throughthe first and second active contact holes 223 a and 223 b, and thesecond ohmic contact layer 227 b is connected to the side portions ofthe second active layer 215 b through the third and fourth activecontact holes 223 c and 223 d. A first source electrode 233 a and afirst drain electrode 236 a spaced apart from each other are formed onthe first ohmic contact layer 227 a, and a second source electrode 233 band a second drain electrode 236 b spaced apart from each other areformed on the second ohmic contact layer 227 b. In addition, a powerelectrode 234 is formed on the second ohmic contact layer 227 b. Thesecond source electrode 233 b extends to the power electrode 234 and thepower electrode 234 is connected to a power line (not shown). Althoughnot shown in FIG. 6, a data line connected to the first source electrode233 a is formed on the interlayer insulating layer 222.

The power electrode 234 and the second gate electrode 205 b overlap eachother with the gate insulating layer 209 and the interlayer insulatinglayer 222 interposed therebetween to constitute a first storagecapacitor StgC1. In addition, the first gate electrode 205 a, the gateinsulating layer 209, the first active layer 215 a, the first ohmiccontact layer 227 a, the first source electrode 233 a and the firstdrain electrode 236 a constitute a switching thin film transistor (TFT)STr, and the second gate electrode 205 b, the gate insulating layer 209,the second active layer 215 b, the second ohmic contact layer 227 b, thesecond source electrode 233 b and the second drain electrode 236 bconstitute a driving TFT DTr.

Further, a first passivation layer 240 of an inorganic insulatingmaterial is formed on the first source electrode 233 a, the first drainelectrode 236 a, the second source electrode 233 b, the second drainelectrode 236 b and the data line. The first passivation layer 240, theinterlayer insulating layer 222 and the gate insulating layer 209include first and second gate contact holes 242 a and 242 b exposing thefirst and second gate electrodes 205 a and 205 b, respectively. Althoughnot shown in FIG. 6, the first passivation layer 240 includes a powercontact hole exposing the power electrode 234 extending from the secondsource electrode 233 b.

A gate line 245 and a gate auxiliary pattern 246 are formed on the firstpassivation layer 240. The gate line 245 crosses the data line to definea pixel region P and is connected to the first gate electrode 205 athough the first gate contact hole 242 a. The gate auxiliary pattern 246is connected to the second gate electrode 205 b through the second gatecontact hole 242 b. In addition, the gate auxiliary pattern 246 overlapsthe power electrode 234 with the first passivation layer 240 interposedtherebetween to constitute a second storage capacitor StgC2. Althoughnot shown in FIG. 6, the power line parallel to the gate line 245 isformed on the first passivation layer 240 and is connected to the powerelectrode 234 through the power contact hole.

Moreover, a second passivation layer 250 of an inorganic insulatingmaterial is formed on the gate line 245 and the gate auxiliary pattern246. The second passivation layer 250 includes an auxiliary contact hole253 exposing the gate auxiliary pattern 246. In addition, the secondpassivation layer 250 and the first passivation layer 240 include firstand second drain contact holes 252 a and 252 b exposing the first andsecond drain electrodes 236 a and 236 b, respectively.

A pixel electrode 270 and a gate connecting electrode 272 each includinga transparent conductive material are formed on the second passivationlayer 250. The pixel electrode 270 is connected to the second drainelectrode 236 b through the second drain contact hole 252 b. Inaddition, the gate connecting electrode 272 is connected to the firstdrain electrode 236 a through the first drain contact hole 252 a and tothe gate auxiliary pattern 246 through the auxiliary contact hole 253.

Although not shown in FIG. 6, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 250 and thegate connecting electrode 272. In addition, an organic luminescent layeris formed on the pixel electrode 270 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 201. The pixel electrode 270, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

In the organic ELD device according to the second embodiment of thepresent invention, since the first and second active layers 215 a and215 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 205 a and 205 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 215 a and 215 b is performed withoutdeformation of the first and second gate electrodes 205 a and 205 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 222 on a centralportion of the first and second active layers 215 a and 215 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 215 a and 215 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 227 a and 227 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 234 extending form the second sourceelectrode 233 b overlaps the second gate electrode 205 b with the gateinsulating layer 209 and the interlayer insulating layer 222 interposedtherebetween to constitute the first storage capacitor StgC1, and thegate auxiliary pattern 246 connected to the second gate electrode 205 boverlaps the power electrode 234 extending from the second sourceelectrode 233 b with the first passivation layer 240 interposedtherebetween to constitute the second storage capacitor StgC2. Since thefirst and second storage capacitors StgC1 and StgC2 are connected to thesecond source electrode 233 b of the driving TFT DTr in parallel, thetotal storage capacitance of the organic ELD device increases.

FIG. 7 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a thirdembodiment of the present invention.

In FIG. 7, a buffer layer 302 of an inorganic insulating material isformed on an entire surface of a substrate 301, and first and secondgate electrodes 305 a and 305 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 302. A gateinsulating layer 309 of an inorganic insulating material is formed onthe first and second gate electrodes 305 a and 305 b, and first andsecond active layers 215 a and 315 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 309. Thefirst and second active layers 315 a and 315 b are formed over the firstand second gate electrodes 305 a and 305 b, respectively.

In addition, an interlayer insulating layer 322 including first tofourth active contact holes 323 a, 323 b, 323 c and 323 d is formed onthe first and second active layers 315 a and 315 b. The first and secondactive contact holes 323 a and 323 b expos side portions of the firstactive layer 315 a, respectively, and the third and fourth activecontact holes 323 c and 323 d expose side portions of the second activelayer 315 b, respectively. First and second ohmic contact layers 327 aand 327 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 322. The first ohmic contact layer 327 a isconnected to the side portions of the first active layer 315 a throughthe first and second active contact holes 323 a and 323 b, and thesecond ohmic contact layer 327 b is connected to the side portions ofthe second active layer 315 b through the third and fourth activecontact holes 323 c and 323 d. A first source electrode 333 a and afirst drain electrode 336 a spaced apart from each other are formed onthe first ohmic contact layer 327 a, and a second source electrode 333 band a second drain electrode 336 b spaced apart from each other areformed on the second ohmic contact layer 327 b. In addition, a powerelectrode 334 is formed on the second ohmic contact layer 327 b. Thesecond source electrode 333 b extends to the power electrode 334 and thepower electrode 334 is connected to a power line (not shown). Althoughnot shown in FIG. 7, a data line connected to the first source electrode333 a is formed on the interlayer insulating layer 322.

The power electrode 334 and the second gate electrode 305 b overlap eachother with the gate insulating layer 309 and the interlayer insulatinglayer 322 interposed therebetween to constitute a first storagecapacitor StgC1. In addition, the first gate electrode 305 a, the gateinsulating layer 309, the first active layer 315 a, the first ohmiccontact layer 327 a, the first source electrode 333 a and the firstdrain electrode 336 a constitute a switching thin film transistor (TFT)STr, and the second gate electrode 305 b, the gate insulating layer 309,the second active layer 315 b, the second ohmic contact layer 327 b, thesecond source electrode 333 b and the second drain electrode 336 bconstitute a driving TFT DTr.

Further, a first passivation layer 340 of an inorganic insulatingmaterial is formed on the first source electrode 333 a, the first drainelectrode 336 a, the second source electrode 333 b, the second drainelectrode 336 b and the data line. The first passivation layer 340, theinterlayer insulating layer 322 and the gate insulating layer 309include first and second gate contact holes 342 a and 342 b exposing thefirst and second gate electrodes 305 a and 305 b, respectively. Althoughnot shown in FIG. 7, the first passivation layer 340 includes a powercontact hole exposing the power electrode 334 extending from the secondsource electrode 333 b.

A gate line 345 and a gate auxiliary pattern 346 are formed on the firstpassivation layer 340. The gate line 345 crosses the data line to definea pixel region P and is connected to the first gate electrode 305 athrough the first gate contact hole 342 a. The gate auxiliary pattern346 is connected to the second gate electrode 305 b through the secondgate contact hole 342 b. Although not shown in FIG. 7, the power lineparallel to the gate line 345 is formed on the first passivation layer340 and is connected to the power electrode 334 through the powercontact hole.

Moreover, a second passivation layer 350 of an inorganic insulatingmaterial is formed on the gate line 345 and the gate auxiliary pattern346. The second passivation layer 350 includes an auxiliary contact hole353 exposing the gate auxiliary pattern 346. In addition, the secondpassivation layer 350 and the first passivation layer 340 include firstand second drain contact holes 352 a and 352 b exposing the first andsecond drain electrodes 336 a and 336 b, respectively.

A pixel electrode 370 and a gate connecting electrode 372 each includinga transparent conductive material are formed on the second passivationlayer 350. The pixel electrode 370 is connected to the second drainelectrode 336 b through the second drain contact hole 352 b. The gateconnecting electrode 372 is connected to the first drain electrode 336 athrough the first drain contact hole 352 a and to the gate auxiliarypattern 346 through the auxiliary contact hole 353. In addition, thegate connecting electrode 372 overlaps the power electrode 334 with thesecond passivation layer 350 and the first passivation layer 340interposed therebetween to constitute a second storage capacitor StgC2.

Although not shown in FIG. 7, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 350 and thegate connecting electrode 372. In addition, an organic luminescent layeris formed on the pixel electrode 370 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 301. The pixel electrode 370, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

In the organic ELD device according to the third embodiment of thepresent invention, since the first and second active layers 315 a and315 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 305 a and 305 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 315 a and 315 b is performed withoutdeformation of the first and second gate electrodes 305 a and 305 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 322 on a centralportion of the first and second active layers 315 a and 315 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 315 a and 315 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 327 a and 327 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 334 extending form the second sourceelectrode 333 b overlaps the second gate electrode 305 b with the gateinsulating layer 309 and the interlayer insulating layer 322 interposedtherebetween to constitute the first storage capacitor StgC1, and thegate connecting electrode 372 connected to the second gate electrode 305b through the gate auxiliary pattern 346 overlaps the power electrode334 extending from the second source electrode 333 b with the secondpassivation layer 350 and the first passivation layer 340 interposedtherebetween to constitute the second storage capacitor StgC2. Since thefirst and second storage capacitors StgC1 and StgC2 are connected to thesecond source electrode 333 b of the driving TFT DTr in parallel, thetotal storage capacitance of the organic ELD device increases.

FIG. 8 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a fourthembodiment of the present invention.

In FIG. 8, a buffer layer 402 of an inorganic insulating material isformed on an entire surface of a substrate 401, and first and secondgate electrodes 405 a and 405 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 402. A gateinsulating layer 409 of an inorganic insulating material is formed onthe first and second gate electrodes 405 a and 405 b, and first andsecond active layers 415 a and 415 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 409. Thefirst and second active layers 415 a and 415 b are formed over the firstand second gate electrodes 405 a and 405 b, respectively.

In addition, an interlayer insulating layer 422 including first tofourth active contact holes 423 a, 423 b, 423 c and 423 d is formed onthe first and second active layers 415 a and 415 b. The first and secondactive contact holes 423 a and 423 b expos side portions of the firstactive layer 415 a, respectively, and the third and fourth activecontact holes 423 c and 423 d expose side portions of the second activelayer 415 b, respectively. First and second ohmic contact layers 427 aand 427 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 422. The first ohmic contact layer 427 a isconnected to the side portions of the first active layer 415 a throughthe first and second active contact holes 423 a and 423 b, and thesecond ohmic contact layer 427 b is connected to the side portions ofthe second active layer 415 b through the third and fourth activecontact holes 423 c and 423 d. A first source electrode 433 a and afirst drain electrode 436 a spaced apart from each other are formed onthe first ohmic contact layer 427 a, and a second source electrode 433 band a second drain electrode 436 b spaced apart from each other areformed on the second ohmic contact layer 427 b. Although not shown inFIG. 8, a data line connected to the first source electrode 433 a isformed on the interlayer insulating layer 422.

The first gate electrode 405 a, the gate insulating layer 409, the firstactive layer 415 a, the first ohmic contact layer 427 a, the firstsource electrode 433 a and the first drain electrode 436 a constitute aswitching thin film transistor (TFT) STr, and the second gate electrode405 b, the gate insulating layer 409, the second active layer 415 b, thesecond ohmic contact layer 427 b, the second source electrode 433 b andthe second drain electrode 436 b constitute a driving TFT DTr.

Further, a first passivation layer 440 of an inorganic insulatingmaterial is formed on the first source electrode 433 a, the first drainelectrode 436 a, the second source electrode 433 b, the second drainelectrode 436 b and the data line. The first passivation layer 440, theinterlayer insulating layer 422 and the gate insulating layer 409include first and second gate contact holes 442 a and 442 b exposing thefirst and second gate electrodes 405 a and 405 b, respectively. Inaddition, the first passivation layer 440 includes source contact hole444 exposing the second source electrode 433 b.

A gate line 445, a gate auxiliary pattern 446 and a power electrode 434are formed on the first passivation layer 440. The gate line 445 crossesthe data line to define a pixel region P and is connected to the firstgate electrode 405 a through the first gate contact hole 442 a. The gateauxiliary pattern 446 is connected to the second gate electrode 405 bthrough the second gate contact hole 442 b. In addition, the powerelectrode 434 is connected to the second source electrode 433 b throughthe source contact hole 444 and is connected to a power line (notshown). The power electrode 434 and the second gate electrode 405 boverlap each other with the gate insulating layer 409, the interlayerinsulating layer 422 and the first passivation layer 440 interposedtherebetween to constitute a first storage capacitor StgC1. Although notshown in FIG. 8, the power line parallel to the gate line 445 is formedon the first passivation layer 440 and is connected to the powerelectrode 434.

Moreover, a second passivation layer 450 of an inorganic insulatingmaterial is formed on the gate line 445, the gate auxiliary pattern 446and the power electrode 434. The second passivation layer 450 includesan auxiliary contact hole 453 exposing the gate auxiliary pattern 446.In addition, the second passivation layer 450 and the first passivationlayer 440 include first and second drain contact holes 452 a and 452 bexposing the first and second drain electrodes 436 a and 436 b,respectively.

A pixel electrode 470 and a gate connecting electrode 472 each includinga transparent conductive material are formed on the second passivationlayer 450. The pixel electrode 470 is connected to the second drainelectrode 436 b through the second drain contact hole 452 b. The gateconnecting electrode 472 is connected to the first drain electrode 436 athrough the first drain contact hole 452 a and to the gate auxiliarypattern 446 through the auxiliary contact hole 453. In addition, thegate connecting electrode 472 overlaps the power electrode 434 with thesecond passivation layer 450 interposed therebetween to constitute asecond storage capacitor StgC2.

Although not shown in FIG. 8, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 450 and thegate connecting electrode 472. In addition, an organic luminescent layeris formed on the pixel electrode 470 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 401. The pixel electrode 470, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

In the organic ELD device according to the fourth embodiment of thepresent invention, since the first and second active layers 415 a and415 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 405 a and 405 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 415 a and 415 b is performed withoutdeformation of the first and second gate electrodes 405 a and 405 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 422 on a centralportion of the first and second active layers 415 a and 415 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 415 a and 415 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 427 a and 427 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 434 connected to the second sourceelectrode 433 b overlaps the second gate electrode 405 b with the gateinsulating layer 409 and the interlayer insulating layer 422 interposedtherebetween to constitute the first storage capacitor StgC1, and thegate connecting electrode 472 connected to the second gate electrode 405b through the gate auxiliary pattern 446 overlaps the power electrode434 extending from the second source electrode 433 b with the secondpassivation layer 450 interposed therebetween to constitute the secondstorage capacitor StgC2. Since the first and second storage capacitorsStgC1 and StgC2 are connected to the second source electrode 433 b ofthe driving TFT DTr in parallel, the total storage capacitance of theorganic ELD device increases.

FIG. 9 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a fifthembodiment of the present invention.

In FIG. 9, a buffer layer 502 of an inorganic insulating material isformed on an entire surface of a substrate 501, and first and secondgate electrodes 505 a and 505 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 502. A gateinsulating layer 509 of an inorganic insulating material is formed onthe first and second gate electrodes 505 a and 505 b, and first andsecond active layers 515 a and 515 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 509. Thefirst and second active layers 515 a and 515 b are formed over the firstand second gate electrodes 505 a and 505 b, respectively.

In addition, an interlayer insulating layer 522 including first tofourth active contact holes 523 a, 523 b, 523 c and 523 d is formed onthe first and second active layers 515 a and 515 b. The first and secondactive contact holes 523 a and 523 b expos side portions of the firstactive layer 515 a, respectively, and the third and fourth activecontact holes 523 c and 523 d expose side portions of the second activelayer 515 b, respectively. First and second ohmic contact layers 527 aand 527 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 522. The first ohmic contact layer 527 a isconnected to the side portions of the first active layer 515 a throughthe first and second active contact holes 523 a and 523 b, and thesecond ohmic contact layer 527 b is connected to the side portions ofthe second active layer 515 b through the third and fourth activecontact holes 523 c and 523 d. A first source electrode 533 a and afirst drain electrode 536 a spaced apart from each other are formed onthe first ohmic contact layer 527 a, and a second source electrode 533 band a second drain electrode 536 b spaced apart from each other areformed on the second ohmic contact layer 527 b. In addition, a powerelectrode 534 is formed on the second ohmic contact layer 527 b. Thesecond source electrode 533 b extends to the power electrode 534 and thepower electrode 534 is connected to a power line (not shown). Althoughnot shown in FIG. 9, a data line connected to the first source electrode533 a is formed on the interlayer insulating layer 522.

The power electrode 534 and the second gate electrode 505 b overlap eachother with the gate insulating layer 509 and the interlayer insulatinglayer 522 interposed therebetween to constitute a first storagecapacitor StgC1. In addition, the first gate electrode 505 a, the gateinsulating layer 509, the first active layer 515 a, the first ohmiccontact layer 527 a, the first source electrode 533 a and the firstdrain electrode 536 a constitute a switching thin film transistor (TFT)STr, and the second gate electrode 505 b, the gate insulating layer 509,the second active layer 515 b, the second ohmic contact layer 527 b, thesecond source electrode 533 b and the second drain electrode 536 bconstitute a driving TFT DTr.

Further, a first passivation layer 540 of an inorganic insulatingmaterial is formed on the first source electrode 533 a, the first drainelectrode 536 a, the second source electrode 533 b, the second drainelectrode 536 b and the data line. The first passivation layer 540, theinterlayer insulating layer 522 and the gate insulating layer 509include first and second gate contact holes 542 a and 542 b exposing thefirst and second gate electrodes 505 a and 505 b, respectively. Inaddition, the first passivation layer 540 includes a first drain contacthole 552 a exposing the first drain electrode 536 a.

A gate line 545 and a gate auxiliary pattern 546 are formed on the firstpassivation layer 540. The gate line 545 crosses the data line to definea pixel region P and is connected to the first gate electrode 505 athrough the first gate contact hole 542 a. The gate auxiliary pattern546 is connected to the first drain electrode 536 a through the firstdrain contact hole 552 b and is connected to the second gate electrode505 b through the second gate contact hole 542 b. In addition, the gateauxiliary pattern 546 connected to the second gate electrode 505 boverlaps the power electrode 534 extending from the second sourceelectrode 533 b with the first passivation layer 540 interposedtherebetween to constitute a second storage capacitor StgC2. Althoughnot shown in FIG. 9, the power line parallel to the gate line 545 isformed on the first passivation layer 540 and is connected to the powerelectrode 534 through the power contact hole.

Moreover, a second passivation layer 550 of an inorganic insulatingmaterial is formed on the gate line 545 and the gate auxiliary pattern546. The second passivation layer 550 and the first passivation layer540 include a second drain contact hole 552 b exposing the second drainelectrode 536 b. A pixel electrode 570 including a transparentconductive material is formed on the second passivation layer 550. Thepixel electrode 570 is connected to the second drain electrode 536 bthrough the second drain contact hole 552 b.

Although not shown in FIG. 9, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 550 and thegate connecting electrode 572. In addition, an organic luminescent layeris formed on the pixel electrode 570 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 501. The pixel electrode 570, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

In the organic ELD device according to the fifth embodiment of thepresent invention, since the first and second active layers 515 a and515 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 505 a and 505 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 515 a and 515 b is performed withoutdeformation of the first and second gate electrodes 505 a and 505 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 522 on a centralportion of the first and second active layers 515 a and 515 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 515 a and 515 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 527 a and 527 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 534 extending from the second sourceelectrode 533 b overlaps the second gate electrode 505 b with the gateinsulating layer 509 and the interlayer insulating layer 522 interposedtherebetween to constitute the first storage capacitor StgC1, and thegate auxiliary pattern 546 connected to the second gate electrode 505 boverlaps the power electrode 534 extending from the second sourceelectrode 533 b with the first passivation layer 540 interposedtherebetween to constitute the second storage capacitor StgC2. Since thefirst and second storage capacitors StgC1 and StgC2 are connected to thesecond source electrode 533 b of the driving TFT DTr in parallel, thetotal storage capacitance of the organic ELD device increases.

FIG. 10 is a cross-sectional view showing an array substrate for anorganic electroluminescent display device according to a sixthembodiment of the present invention.

In FIG. 10, a buffer layer 602 of an inorganic insulating material isformed on an entire surface of a substrate 601, and first and secondgate electrodes 605 a and 605 b each including an impurity-dopedpolycrystalline silicon are formed on the buffer layer 602. A gateinsulating layer 609 of an inorganic insulating material is formed onthe first and second gate electrodes 605 a and 605 b, and first andsecond active layers 615 a and 615 b each including an intrinsicpolycrystalline silicon are formed on the gate insulating layer 609. Thefirst and second active layers 615 a and 615 b are formed over the firstand second gate electrodes 605 a and 605 b, respectively.

In addition, an interlayer insulating layer 622 including first tofourth active contact holes 623 a, 623 b, 623 c and 623 d is formed onthe first and second active layers 615 a and 615 b. The first and secondactive contact holes 623 a and 623 b expos side portions of the firstactive layer 615 a, respectively, and the third and fourth activecontact holes 623 c and 623 d expose side portions of the second activelayer 615 b, respectively. First and second ohmic contact layers 627 aand 627 b of impurity-doped amorphous silicon are formed on theinterlayer insulating layer 622. The first ohmic contact layer 627 a isconnected to the side portions of the first active layer 615 a throughthe first and second active contact holes 623 a and 623 b, and thesecond ohmic contact layer 627 b is connected to the side portions ofthe second active layer 615 b through the third and fourth activecontact holes 623 c and 623 d. A first source electrode 633 a and afirst drain electrode 636 a spaced apart from each other are formed onthe first ohmic contact layer 627 a, and a second source electrode 633 band a second drain electrode 636 b spaced apart from each other areformed on the second ohmic contact layer 627 b. In addition, a powerelectrode 634 is formed on the second ohmic contact layer 627 b. Thesecond source electrode 633 b extends to the power electrode 634 and thepower electrode 634 is connected to a power line (not shown). Althoughnot shown in FIG. 10, a data line connected to the first sourceelectrode 633 a is formed on the interlayer insulating layer 622.

The power electrode 634 and the second gate electrode 605 b overlap eachother with the gate insulating layer 609 and the interlayer insulatinglayer 622 interposed therebetween to constitute a first storagecapacitor StgC1. In addition, the first gate electrode 605 a, the gateinsulating layer 609, the first active layer 615 a, the first ohmiccontact layer 627 a, the first source electrode 633 a and the firstdrain electrode 636 a constitute a switching thin film transistor (TFT)STr, and the second gate electrode 605 b, the gate insulating layer 609,the second active layer 615 b, the second ohmic contact layer 627 b, thesecond source electrode 633 b and the second drain electrode 636 bconstitute a driving TFT DTr.

Further, a first passivation layer 640 of an inorganic insulatingmaterial is formed on the first source electrode 633 a, the first drainelectrode 636 a, the second source electrode 633 b, the second drainelectrode 636 b and the data line. The first passivation layer 640, theinterlayer insulating layer 622 and the gate insulating layer 609include first and second gate contact holes 642 a and 642 b exposing thefirst and second gate electrodes 605 a and 605 b, respectively. Inaddition, the first passivation layer 640 includes a first drain contacthole 652 a exposing the first drain electrode 636 a.

A gate line 645 and a gate auxiliary pattern 646 are formed on the firstpassivation layer 640. The gate line 645 crosses the data line to definea pixel region P and is connected to the first gate electrode 605 athrough the first gate contact hole 642 a. The gate auxiliary pattern646 is connected to the first drain electrode 636 a through the firstdrain contact hole 652 b and is connected to the second gate electrode605 b through the second gate contact hole 642 b. In addition, the gateauxiliary pattern 646 connected to the second gate electrode 605 boverlaps the power electrode 634 extending from the second sourceelectrode 633 b with the first passivation layer 640 interposedtherebetween to constitute a second storage capacitor StgC2. Althoughnot shown in FIG. 10, the power line parallel to the gate line 645 isformed on the first passivation layer 640 and is connected to the powerelectrode 634 through the power contact hole.

Moreover, a second passivation layer 650 of an inorganic insulatingmaterial is formed on the gate line 645 and the gate auxiliary pattern646. The second passivation layer 650 and the first passivation layer640 include a second drain contact hole 652 b exposing the second drainelectrode 636 b and a source contact hole 662 exposing the second sourceelectrode 633 b. A pixel electrode 670 and a capacitor auxiliary pattern680 each including a transparent conductive material are formed on thesecond passivation layer 650. The pixel electrode 670 is connected tothe second drain electrode 636 b through the second drain contact hole652 b, and the capacitor auxiliary pattern 680 is connected to thesecond source electrode 633 b through the source contact hole 662. Inaddition, the capacitor auxiliary pattern 680 connected to the secondsource electrode 633 b overlaps the gate auxiliary pattern 646 connectedto the second gate electrode 605 b with the second passivation layer 650interposed therebetween to constitute a third storage capacitor StgC3.

Although not shown in FIG. 10, a bank of one of inorganic and organicinsulating materials is formed at a boundary portion of the pixel regionP. The bank may be formed on the second passivation layer 650 and thegate connecting electrode 672. In addition, an organic luminescent layeris formed on the pixel electrode 670 and a reference electrode is formedon the organic luminescent layer. The organic luminescent layer emitsone of red, green and blue colored lights and the organic luminescentlayers emitting different colored lights may be alternately disposed inthe pixel regions P. The reference electrode may be formed over anentire surface of the substrate 601. The pixel electrode 670, theorganic luminescent layer and the reference electrode in the pixelregion P constitute an organic electroluminescent (EL) diode.

In the organic ELD device according to the sixth embodiment of thepresent invention, since the first and second active layers 615 a and615 b include intrinsic polycrystalline silicon, a mobility of theswitching TFT STr and the driving TFT DTr is improved. In addition,since the first and second gate electrodes 605 a and 605 b includeimpurity-doped polycrystalline silicon, the crystallization step for thefirst and second active layers 615 a and 615 b is performed withoutdeformation of the first and second gate electrodes 605 a and 605 b anda polycrystalline silicon TFT having a bottom gate structure isobtained. Further, the interlayer insulating layer 622 on a centralportion of the first and second active layers 615 a and 615 b functionsas an etch stopper for a channel region. Accordingly, the first andsecond active layers 615 a and 615 b have a uniform thickness anddeterioration of the switching TFT STr and the driving TFT DTr due tothe thickness difference is prevented. Moreover, since the first andsecond ohmic contact layers 627 a and 627 b are formed of impurity-dopedamorphous silicon, a doping step using an ion implantation apparatus isomitted and initial investment for an additional apparatus is reduced.

Further, the power electrode 634 extending from the second sourceelectrode 633 b overlaps the second gate electrode 605 b with the gateinsulating layer 609 and the interlayer insulating layer 622 interposedtherebetween to constitute the first storage capacitor StgC1, the gateauxiliary pattern 646 connected to the second gate electrode 605 boverlaps the power electrode 634 extending from the second sourceelectrode 633 b with the first passivation layer 640 interposedtherebetween to constitute the second storage capacitor StgC2, and thecapacitor auxiliary pattern 680 connected to the second source electrode633 b overlaps the gate auxiliary pattern 646 connected to the secondgate electrode 605 b with the second passivation layer 650 interposedtherebetween to constitute the third storage capacitor StgC3. Since thefirst, second and third storage capacitors StgC1, StgC2 and StgC3 areconnected to the second source electrode 633 b of the driving TFT DTr inparallel, the total storage capacitance of the organic ELD deviceincreases.

Although an array substrate for an organic electroluminescent displaydevice is illustrated in first to sixth embodiments of the presentinvention, the structure and the fabricating method of the TFT of thefirst to sixth embodiments can be applied to an array substrate foranother display device such as a liquid crystal display device. Forexample, the pixel electrode may be connected to the switching TFTwithout the driving TFT in the array substrate for an LCD device.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method of fabricating adisplay device using a plastic substrate of the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An array substrate for a display device,comprising: a substrate; first and second gate electrodes ofimpurity-doped polycrystalline silicon on the substrate; a gateinsulating layer on the first and second gate electrodes; first andsecond active layers of intrinsic polycrystalline silicon on the gateinsulating layer, the first and second active layers corresponding tothe first and second gate electrodes, respectively; an interlayerinsulating layer on the first and second active layers and includingfirst to fourth active contact holes, the first and second activecontact holes exposing side portions of the first active layer, thethird and fourth active contact holes exposing side portions of thesecond active layer; first and second ohmic contact layers ofimpurity-doped amorphous silicon on the interlayer insulating layer, thefirst ohmic contact layer contacting the first active layer through thefirst and second active contact holes, the second ohmic contact layercontacting the second active layer through the third and fourth activecontact hole; first source and drain electrodes on the first ohmiccontact layer and second source and drain electrodes on the second ohmiccontact layer; a data line on the interlayer insulating layer, the dataline connected to the first source electrode; a first passivation layeron the first source and drain electrodes, the second source and drainelectrodes and the data line; a gate line and a gate auxiliary patternon the first passivation layer, the gate line connected to the firstgate electrode and crossing the data line to define a pixel region, thegate auxiliary pattern electrically connected to the first drainelectrode and the second gate electrode by a transparent conductive gateconnecting electrode; a second passivation layer on the gate line; and apixel electrode on the second passivation layer, the pixel electrodeconnected to the second drain electrode.
 2. The substrate according toclaim 1, further comprising: a power electrode connected to the secondsource electrode; and a power line on the first passivation layer, thepower line connected to the power electrode.
 3. The substrate accordingto claim 2, wherein the gate insulating layer, the interlayer insulatinglayer and the first passivation layer include first and second gatecontact holes exposing the first and second gate electrodes,respectively, wherein the gate line is connected to the first gateelectrode through the first gate contact hole and the gate auxiliarypattern is connected to the second gate electrode through the secondgate contact hole.
 4. The substrate according to claim 3, furthercomprising a gate connecting electrode on the second passivation layer,wherein the first and second passivation layers include first and seconddrain contact holes exposing the first and second drain electrodes,respectively, and the second passivation layer includes an auxiliarycontact hole exposing the gate auxiliary pattern, and wherein the gateconnecting electrode is connected to the first drain electrode throughthe first drain contact hole and to the gate auxiliary pattern throughthe auxiliary contact hole, and the pixel electrode is connected to thesecond drain electrode through the second drain contact hole.
 5. Thesubstrate according to claim 4, wherein the power electrode is formed onthe interlayer insulating layer and extends from the second sourceelectrode, and the power electrode overlaps the second gate electrode toconstitute a first storage capacitor with the gate insulating layer andthe interlayer insulating layer interposed therebetween.
 6. Thesubstrate according to claim 5, wherein the gate auxiliary patternoverlaps the power electrode to constitute a second storage capacitorwith the first passivation layer interposed therebetween.
 7. Thesubstrate according to claim 1, further comprising a buffer layerbetween each of the first and second gate electrodes and the substrate,wherein the buffer layer includes an inorganic insulating material. 8.The substrate according to claim 1, further comprising a barrier layerunder the first and second ohmic contact layers, wherein the barrierlayer includes intrinsic amorphous silicon and has the same shape as thefirst and second ohmic contact layers.